This invention relates to a fastener for use in interference fit holes to produce a fatigue resistant joint in highly stressed structures such as aircraft wings. It is well known in the art and can be seen in Wing U.S. Pat. Nos. 8,138,987 and 8,390,906 that fatigue resistant fasteners having a head, a smooth shank, an external thread and an internal wrenching feature coaxial with and at the same end as the thread are well known in the art of aircraft fastening. However, this fastener has problems when it is installed in interference fit holes.
The internal wrenching feature becomes unnecessary because the friction of the interference fit will prevent the fastener pin from turning when installing threaded nuts even when self locking friction devices are tightened onto the threaded end of the pin.
However, then the pin must be pounded into the hole using air hammers or presses using high forces which can deflect the structure or produce noise that is unacceptable in the modern industrial environment.
As an alternative method of interference fit installation, it is well known in the art to make a fastener pin with a pull stem protruding from the threaded, or grooved, end for applying a pulling force to install the pin in an interference fit hole in structure. Such devices are shown in many Jason U.S. Pat. No. 4,221,152, Schuster U.S. Pat. No. 2,955,505 and Dixon U.S. Pat. No. 4,324,518. In all of the prior art the pull stem requires an extra length of material which involves extra cost of production, that become particularly significant in fasteners manufactured from exotic metals such as titanium alloys. In this intent invention, the pulling mandrel can be from a cheaper, stronger material than the fastener pin, and can use more efficient manufacturing means to lower the cost further. Re-use of the pulling mandrel can be instituted if economically favorable.
Further, using the pin of this invention, a tool as shown in Wing et al Pat. No. 2,789,619 can be used with an integrated mandrel to rotate the mandrel into the threaded hole of the pin, pull the pin into interference fit and rotate the mandrel out of engagement with the fastener pin, and this patent is incorporated wherein in its entirety by reference to show a suitable tool for the purpose.
An object of this invention is to provide a fastener pin with an internally threaded hole coaxial with the thread of the pin to which a mandrel can be engaged to pull the fastener threaded pin into interference fit with a workpiece hole.
A further object of this invention is to provide a hardened mandrel for engagement with the threaded hole in the pin to be used to pull the pin into interference engagement with a workpiece fastener hole.
Another object of this invention is to provide a safety groove in the hardened installation mandrel which safety groove will fail the mandrel before damaging the head of the fastener pin by tensile overload in installation.
Another object of this invention is to provide means on the mandrel to engage a power tool for installation of the fastener.
A further object of this invention is to adapt power tool means to engage the tapped hole in the fastener threaded end for pulling the fastener into an interference fit.
The above and other features of the invention will be fully understood from the following detailed description and the accompanying drawings, in which: